Most people know of the Irish potato blight of the 1840s, which caused widespread famine among a population that relied on potatoes as a staple part of its diet.

Perhaps fewer people know the blight was caused by a type of crop pest called an oomycete, which looks a little like a fungus. Even today, this category of pathogen is responsible for significant losses in the world's potato crops.

And because of climate change, it and many other crop pests and pathogens are spreading.

That's the message of a paper released Sunday in the journal Nature Climate Change.

The study, the first to take a mathematical approach to determine the spread of pathogens over the past half-century, found that on average, crop pests and pathogens in the Northern Hemisphere have moved northward by about 1.7 miles per year since 1960.

"If you look at all pests and pathogens, they are moving," said Sarah Gurr, one of the paper's authors and a fungal biologist formerly at the University of Oxford and now at the University of Exeter.

But that's just an average. Two of the most concerning types of crop pathogens -- fungi, which cause diseases in many staple crops, and those blight-causing oomycetes -- are moving northward at closer to 4 miles per year, Gurr said.

"The major crops that feed the world are rice and wheat and maize and then potatoes," she said. "If you look at the major pathogens of all these, they are either all fungi or fungal-like creatures, the oomycetes."

Gurr and her co-authors were able to document this shift using a rich database of pest observations reported to CABI, an international development organization.

Some crops will be at risk
Because wealthier countries are likely to have better pest and pathogen reporting than poor countries, the group of scientists had to take that and other factors, like the country's land area and amount of land in agricultural production, to remove observational bias in the numbers.

"We went to considerable statistical trouble," Gurr said.

Lynne Boddy, a fungal ecologist from the University of Exeter who was familiar with the paper, has also noted that fungi are changing with the climate. She's documented changes in fruiting time in fungi, due to climate change.

"We know that considerable changes are going on," Boddy said.

This paper is "very important," she added, because so little is known about fungi generally and particularly about how fungi, which play a key role in natural and agricultural ecosystems, will change in a warming world.

These changes might soon affect vast parts of the world's food supply. Gurr's results indicate that crops in the Northern Hemisphere will encounter pathogens they have not seen before.

"If you are standing in a wheat field in North America or Canada, it's hectare upon hectare of genetically uniform wheat with perhaps one resistance gene to hold back the march of fungi. It will not necessarily have the right resistance genes for pathogens that are moving," she said.

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